1. Field of the Invention
The present invention relates to methods for sealing together substrates having high coefficients of thermal expansion. More particularly, the present invention relates to a method for sealing together several glass sheets with a frit to form a glass package suitable for housing an electrical or electronic device, wherein a large difference in CTE exists between the glass sheets and the frit.
2. Technical Background
Many electronic or photonic devices that are environmentally sensitive may benefit from the use of glass packages that can be hermetically sealed. Such devices include photovoltaic devices, organic light emitting diode (OLED) displays, OLED lighting panels, plasma displays, surface conduction electron emitter displays (SEDs) and field emission displays (FEDs) to name but a few. For example, the electroluminescent organic materials comprising OLED displays or organic lighting panels are subject to degradation if exposed to moisture or oxygen, and thus must be protected from such exposure. Moreover, the display is expected to have a service lifetime of many tens of thousands of hours. To achieve these goals many OLED displays are sealed using a glass sealing frit disposed between the glass sheets. The individual glass substrate sheets are typically less than about 0.7 mm in thickness, and with a separation between the two sheets of the order of 15-20 μm.
The manufacture of OLED displays requires precise alignment of the various components, for example alignment of the two glass substrates. Dimensional changes in the substrates can be detrimental to the assembly process. For this reason, glass substrates having high strain points and low coefficients of thermal expansion (CTE) are used. To achieve a robust seal between the sheets, a sealing frit is used that has a CTE substantially equal to the CTEs of the substrates. Other devices, on the other hand, can be more tolerant of imperfections, such as OLED lighting panels. As a consequence, lower cost, relatively high CTE glasses are being considered for these applications. It would be advantageous if frits developed for the OLED display industry could be applied to these new applications without significant modification. However, sealing low CTE frits to high CTE substrates poses an enormous challenge.